Abstract: Compared with high-rate denial of service attacks, low-rate denial of service attack is hard to detect by the existing intrusion detection systems, because it is much more concealed. The network performance with low-rate attacks in different environments was analyzed; two novel dynamic adjusting strategies for retransmission timeout were also proposed. Experiments indicate that the proposed method can effectively fight off low-rate denial of service attacks. Compared with the strategy currently used on the Internet, it can enhance the network throughput above 300% when the attack period is less than 2 seconds.